Nanoparticles have been broadly defined as particles having one or more dimensions of the order of 100 nm or less. Even though various materials such as polymers, ceramics, metals and organic molecules are being currently investigated for developing nanosized particles, metal nanoparticles have raised significant interest due to their unique properties.
Nanosized metallic particles, mainly gold and silver nanoparticles, have attracted attention because of their unique optical and electrical properties, as well as potential biomedical applications. Thus, depending upon their size, shape, surface area, surface plasmon and surface chemistry, these metallic nanoparticles are known to show distinct optical, magnetic, electrical and biological properties which are different from the bulk materials [1].
Due to their unique properties and various areas of applications such as infection resistance, catalysis, nanoelectronics, optical filters and surface raman scattering, nanoparticles of silver are one of the most extensively investigated metallic nanoparticles [2]. Several techniques have already been developed to form metal nanoparticles in solution. Thus, silver nanoparticles are commonly prepared by the controlled reduction of silver salt solutions. The structure and corresponding physical, chemical, and biological properties of silver nanoparticles are known to strongly depend on the method of preparation and the experimental conditions [3]. Several reduction techniques have been investigated. These reduction techniques include strong chemical reducing agents such as sodium borohydride and hydrazine, irradiation using gamma rays, ultra violet, and visible light, microwave as well as ultra sound, and weak reducing agents such as ascorbates, citrates, alcohol, as well as polyols.
Even though colloidal solutions of silver exhibit unique optical and biological properties, the assembly of these particles into thin films is highly recommended for the development of practical applications [4]. Recently, techniques have been developed to immobilize silver nanoparticles on surfaces via surface modification techniques [5].
Various preparation routes for composite materials have been proposed.
These include self assembly [6], electroless plating [7], layer by layer (LBL) self assembly of polyelectrolytes and metal nanoparticles [8] and ultra sound irradiation [9]. Most of these approaches tend to produce surfaces coated with metal nanoparticles by physical adsorption or electrostatic interactions and are not highly suitable for practical biomedical applications. Recently, physical vapor deposition or magnetron sputtering has been investigated to develop thin nanostructured silver surfaces for a variety of applications. A radiofrequency magnetron source is commonly used for the sputtering process to deposit porous nanocrystalline metallic silver on surfaces.
A surface produced by magnetron sputtering of silver has been shown to have strong antibacterial properties [10]. The antibacterial property has been attributed to the release of silver ions from the surface in a controlled and appropriate concentration. In addition to antibacterial properties, the modified surface has wound healing properties, demonstrating the advantages of silver coated materials for biomedical applications [11]. Even though it is highly effective, the fabrication process has several limitations to be used for practical applications. These include the lack of flexibility and controllability of the process, the limited range of materials that can be modified and the limited surface area that can be modified at a time.
There is a long felt need in the art for compositions and methods by which surface modification techniques can be used to modify wide range polymeric substrates using metal nanoparticles as well as for metallic substrates. The present invention satisfies these needs.